SYMBIOSIS-What They Don’t Teach You in School

By Michael Wade

Symbiosis is an intimate relationship between two organisms where both organisms benefit directly from each other. Most symbiosis occurs between plants or animals and microbes. We have symbiotic bacteria in our guts that break down food into smaller molecules that our intestinal cells can absorb and the bacteria in return get food and a protective environment. Establishing a symbiotic relationship among many different animals (vertebrates and invertebrates) with their microbial counterparts is an important relationship that is detrimental to the fitness of the host.

Figure 1: Complexity of gut microbiota contributions to host physiology

The role of symbiotic relationships goes beyond just a beneficial one-in some situations, the host actually requires infection of microbes in order for that infected tissue to develop properly! An example of this is seen in germ-free rats in a sterile environment. The beginning of the large intestine, or the cecum, is enlarged in germ-free rats, and has been attributed to reproductive and functional gastrointestinal disorders. Germ-free mice also have problems absorbing nutrients due to a reduction in the villous capillary networks in the GI tract, have a smaller surface area of gut, have abnormal bile acid metabolism and have a reduced rate in systemic cholesterol metabolism. In invertebrate species, such as the Hawaiian bobtail squid Euprymna scolopes, a restructuring of the light organ crypt is seen that is similar to that in the GI tract of mice once its symbiont, Vibrio fischeri, establishes an infection. In the crypt, the epithelial cells swell and increase microvillar density and increase mucus secretion. However, there are also changes to remote tissues that don’t interact directly with V. fischeri, such as surface epithelial fields and ducts, to undergo remodeling by inducing apoptosis in these cells. There is also a gradual loss of surface ciliated epithelium that occurs post infection.

 Figure 2. Regression of ciliated epithelialium post V. fischeri infection (top) and remodeling of light organ (bottom).

Like in Euprymna scolopes, gut microbes in mammals affect the development of systems outside the GI tract. The cardiovascular system in germ-free mice is impaired in several ways, including a decreased cardiac output, and a reduced myocardial weight. The nervous system is also abnormal and underdeveloped in these mice. There is also evidence that the gut microbiota play a role in brain development and behavior, and can lead to brain disorders including reduced anxiety and an abnormal stress response. In humans, the gut microbiota has been linked to autism, Alzheimer’s, and Huntington’s disease in that patients with autism have unusual levels of gut microbiota, and patients with Alzheimer’s or their gut microbiota have a greater propensity to metabolize bile acids.

Figure 3. Comparison of abdomen of germ-free (left) and normal (right)

There is a misconception, even within the scientific community, that the role of the immune system is to fight pathogens and remove them from the host. However, that statement has been shown in many cases to be an inaccurate description. In fact, the immune system (both the adaptive and innate immune system) REQUIRES bacteria in order to develop properly. Germ-free animals have shown to have a number of adaptive immune response problems, including poorly formed spleens and lymph nodes, abnormal numbers of immune cell types, decreased lymphoid follicles, and decreased secreted IgA and IgG.

 Figure 4: Overview of some interactions with gut microbiota and host immune system

The adaptive immune system of germ-free mice is underdeveloped. There is a lack of CD4+ T helper cells, and T17 cells, which is reversible, both locally and systemically, upon the addition of only one strain of gut bacteria (which later was shown to be a capsular antigen). This is amazing considering that many different species of bacteria reside in the gut of mice, but only the presence of one bacterial species triggers the development and balance (cell types, cell numbers, and proper cytokines) of the adaptive immune response through a specific dendritic cell. In invertebrate species that lack an adaptive immune system, like the Hawaiian bobtail squid Euprymna scolopes, the phagocytic response of the innate immune system changes only after Vibrio fischeri colonizes the light organ.

As we investigate the role of symbiosis, we find more and more interesting connections between the host and its microbiota. The establishment of the symbiotic microbes at a young age is of great importance in that some of the developmental changes that arise after infection are irreversible after a certain point.  There are many more interesting stories of symbiosis, but telling them all would be a lengthy task. A couple of those topics include links to obesity, inflammatory bowel disease, liver disease, allergies, type 1 diabetes and cell-cell signaling(host-resident micobiota, resident-pathogen, and host-pathogen signaling).

References:

Nyholm, S.V., and M.J. McFall-Ngai. 2004. The Winnowing-Establishing the Squid-Vibrio Symbiosis. Nature 2:632-642.

Sekirov, I., Russel, S.L.,Antunes, L.C.M., and Brett Finlay. 2010. Gut microbiota in health and disease. Physiological Reviews. 3:859-904.

Collins, A.J., Schleicher, T.R., Rader, B.A., and Spencer V. Nyholm. 2010. Understanding the role of hemocytes in a squidVibrio symbiosis using transcriptomics and proteomics. Frontiers in Immunoogy. 3:1-14.

Gross, R., Vavre, F., Heddi, A., Hurst, G. D. D., Zchori-Fein, E., and Kostas Bourtzis. 2009. Immunity and symbiosis. Molecular Microbiology. 73:751-759.

Images:

Figure 1: Gut microbiota in health and disease

Figure 2: The Winnowing-Establishing the Squid-Vibrio Symbiosis (top) Mcro 424 lecture PDF

Figure 3: http://www.narl.org.tw/en/topic/topic.php?topic_id=1

Figure 4: http://www.aat-taa.eu/index/en/research/host-bacteria-interaction.html

A Cold Wet Nose

By Andrea DeBrish

It’s a great feeling, you come home from work and there at the door waiting for you is your dog. They jump around and push their cold nose against your hand, vying for affection. For dogs their nose is of great significance. As a species they rely heavily on smell for identification and socializing. They can detect scents far beyond what we can.

How do they do it?

At first glance from the outside a dogs nose does not seem that different from ours. They have two nostrils and a nasal cavity. Their nasal cavity extends farther than ours though and has turbinate bones on the upper side increasing surface area for olfactory epithelium. (Olfactory= relating to the sense of smell, epithelium=a membranous tissue). Olfactory receptor cells are spread throughout this epithelium. Of these receptors dogs have approximately 300 million in comparison to our 6 million (Olfactory receptor=receive an odorant). These olfactory receptors are on the surface of olfactory neurons which initiate the movement of the signal to the brain, specifically the olfactory lobe. (Dogs have a much larger olfactory bulb than humans). The cold wet nature of a dogs nose helps to dissolve different molecules in the air, bringing them to the specialized olfactory epithelium.

Sniffing in dogs is the action of quick short inhalations and exhalations in series. The upper surface of the dogs nose creates a pocket,under the bony subethmoidal shelf (just a bony shelf) where odor molecules will accumulate between sniffs to increase the intensity and the likelhihood of detection. They also split the flow of air as it comes in between the lungs and the olfactory sensors. A majority of the air passes down towards their lungs for respiration but about 12 percent is kept behind in the pocket. Here it is filtered through bony structures called turbinates which separate out the odor molecules based on chemical properties. Olfactory tissues lining the turbinates will eventually bind the odorants and pass on the signal.

As air exits the nose of a dog it travels via flaps to the side of the nose to increase the rate of smelling for new scents by ushering in the new scents. These improvements over our own nasal sensory system have increased their detection rate to around 100,000 times greater than our own. An analogy for their greatly increased sense of smell-If a person can see around three miles on a clear day, a dog would be able to see 3000 miles if their eye sight were better than ours at the same relative rate for which their sense of smell is better.

Dogs have a second area for sensing smells, the vomeronasal organ which also has olfactory epithelium. It is still unclear whether the vomeronasal organ is responsible solely for pheromone detection in dogs. This organ contains two fluid filled sacs and also sends it impulses to the hypothalamus, a region associated with sexual and social behaviours. 

The receptor neurons of the nasal cavity and the vomeronasal are different from one another. In the nasal cavity, each receptor neuron ends with a dendrite with several thin mucus covered cilia (hair like projections). The receptors for the vomeronasal organ usually do not have cilia but do have microvilli (microscopic cellular membrane protrusions). 

So Where did your dog get this great sense of smell?

The ancestor of your pet dog is the wolf. In the wild wolves follow their noses when on the trail of their prey until it is within sight. They will then switch to sight to finish the chase.

There is some research currently suggesting the acuity of a dogs sense of smell may come from their olfactory receptors, and not simply because they have more of them. The olfactory receptors are members of the G protein-coupled receptor superfamily. This means they have 7 transmembrane domains (where the protein crosses the membrane). At these loops there is significant polymorphism (varied within the population). This is believed to be related to how frequently an odorant and receptor bind.

Ok, so your dog has a great sense of smell. Why is that important?

Dogs’ sense of smell has been used by people for a long time. They are used to recover people from disaster sites, track crime suspects, detect drugs and bombs in public areas and more recently to aid in detecting illness in humans. There have been multiple studies looking at the rate of success for dogs sniffing out cancer in people. They have tested dogs smelling breath, urine and blood samples.

 They may also be able to alert a person right before they have a seizure or if they are hypoglycemic.

Dogs can be trained relatively quickly (2-3 weeks) to detect cancerous breath samples from non cancerous for breast and lung cancer patients. In that particular study they found canines were accurate for both types. Another study found there was no greater likelihood of the dog detecting cancer than the dog just randomly guessing each time and eventually getting it right. A third study found dogs were able to detect colon cancer from urine samples at a significant rate. There is not yet a definite consensus on the effectiveness of dogs sniffing out different types of cancers.

If dogs are sniffing out cancer it is likely due to patterns of biochemical markers which are exhaled by people with cancer. Their sensitivity has been confirmed at least in part by using gas chromatography/mass spectroscopy to identify some of the volatile chemicals exhaled by cancer patients. (These are chemicals from the cancer, not from cancer treatment) This could allow us to detect cancer a lot sooner and increase chances of survival, finding it in the early stages.

 Even if dogs do not prove reliable, the structure of the dog nose can help to teach us a lot about smelling things. There are engineers working to build machines which can sniff with the accuracy of a dog. These are especially important for dangerous scouting missions including looking for landmines. An e-nose could also have applications in diagnosis for more than just cancer.

So even if you aren’t a person who likes to go home and be greeted by that cold wet nose everyday, that nose is working overtime for our safety as well as for some treats. 

References

 Cornu, J.N., G.C. Tassin, V. Ondet, C. Girardet, and O. Cussenot. 2010. Olfactory detection of prostate cancer by dogs sniffing urine: a step forward in early diagnosis. European Urology 59:197-201.

Correa, J.E. 2011. The dogs sense of smell. Alabama Cooperative Extension System. http://www.aces.edu/pubs/docs/U/UNP-0066/UNP-0066.pdf

Derr, M. 2001. With training, a dog’s nose almost always knows. New York Times. http://www-psych.stanford.edu/~bigopp/Behaviorism.html

Gordon, R.T., C.B. Schatz, L.J. Myers, M. Kosty, C. Gonczy, J. Kroener, M. Tran, P. Kurtzhals, S. Heath, J.A. Koziol, N. Arthur, M. Gabriel, J. Hemping, G. Hemping, S. Nesbitt, L. Tucker-Clark and J. Zaayer. 2008. The use of canines in the detection of human cancers. The Journal of Alternative and Complementary Medicine 14:61-67.

Lesniak, A., M. Walczak, T. Jezierski, M. Sacharczuk, M. Gawkowski and K. Jaszczak. 2008. Canine olfactory receptor gene polymorphism and its relation to odor detection performance by sniffer dogs. Journal of Heredity. 99(5):518-527.

McCulloch, M., T. Jezierski, M. Broffman, A. Hubbard, K. Turner, and T. Janecki. 2006. Diagnostic accuracy of canine scent detection in early- and late-stage lung and breast cancers. Integrative Cancer Therapies 5(1):30-39.

Tyson, P. 2012. Dogs’ Dazzling Sense of Smell. NOVA scienceNOW. http://www.pbs.org/wgbh/nova/nature/dogs-sense-of-smell.html

When Monarchs take flight

Ryan Baker-Branstetter

It's that time of year again.  No, not time to start making spring break plans.  Monarch butterfly overwintering season!  Two weeks ago, I went down to Pismo State Beach and feasted my eyes on thousands of butterflies covering a eucalyptus grove.  There were an estimated 25,000 butterflies there last month during the peak of the season and "only" about 10,000 when I visited.  I wanted to know more and promptly went to the most reliable and important resource on this planet: Wikipedia.  My interest was piqued, so I actually did the research to make this an interesting and hopefully entertaining blog post.

Monarch butterflies at an overwintering site in Mexico

Monarch butterflies (Danaus plexippus) undergo one of the most incredible migrations on Earth.  During the summer, they can be found throughout the northern US, when temperatures are tolerable for this fragile species.  Once fall arrives and the temperature starts to drop, they begin a journey that can span thousands of miles.  There are two general migration patterns that are followed, separated by the continental divide.  Butterflies on the western side of the divide travel to the California coast or down to Baja California, while those on the eastern side winter in Florida and Central Mexico.

 Monarch butterfly migration map

After spending the winter in more favorable conditions, it's time to start the journey north.  If a species that weighs between .27 to .75 grams traveling thousands of miles wasn't amazing enough, here's where it gets really interesting.  It usually takes at least two generations of spring and summer butterflies to reach their original range.  Monarch butterflies "return" to specific geographic areas that they have never actually been that are usually hundreds to thousands of miles away.  Wow.  The next big question is how.

Monarch butterflies use up to three specific systems to navigate their way: sun compass, circadian clock, and possibly magnetic compass.  Primary compass sense is usually attributed to the sun compass, but it needs further navigational aid to orient itself properly as the season changes since the sun is a moving target, but the butterfly is trying to navigate to a fixed point.  Scattered sunlight creates a polarization pattern and gradient of skylight that is received by the butterfly eye for orientation. 

The circadian clock is used to compensate for changing amounts of daylight and is regulated at an mRNA and protein level in the cells of the core clock components.  Research has demonstrated that these structure are located in the antennae (Merlin et al.,2009).  The butterfly's antennae were covered with black paint and then exposed to light conditions similar to Fall.  The butterflies were then flown and the direction that they took was recorded.  Butterflies that were not covered with paint oriented towards the south/south-west, while those with covered antennae moved in a west/north-west direction, demonstrating that the antennae was important in orientation based on changing day lengths.

Sunlight signal transduction pathway in Monarch butterflies

Use of a magnetic compass is another sense that has been implicated in navigation as well. Experimentally generated magnetic fields can induce disorientation.  Interestingly, flight behavior is also disrupted when flown under experimentally cloudy skies, which would seem to be the most useful time to utilize this sense. It has been hypothesized that since his experiment was performed using Plexiglass, which blocks specific light wavelengths, magnetic sense may be mediated by light exposure, but the exact mechanism is still under investigation.

Further questions still stand about the exact mechanisms Monarchs use for navigation. For instance, does the Monarch have an actual "map sense" or do they primarily rely on environmental cues?  Do social interactions have an effect on migration?  What determines the end point of the southward migration? 

Recently published research (Guerra et al., 2013) sheds some light on the effect of environmental factors.  Summer Monarch butterflies in Massachusetts experimentally exposed to colder temperatures that imitated spring-migration signals in Mexico.  They started to migrate northward, even when under daylight conditions that imitated fall-like conditions.  The authors suggested that a strongly temperature dependent system would be probable since temperature is such an influential factor in over-wintering survival.  Overwintering sites typically have low enough temperatures to keep metabolic demands low, but not so cold to cause freezing.  This strong temperature-dependent mechanism has potential for disruption of normal migration patterns due to global warming.

Flight of the Butterflies trailer - 2012 documentary

The yearly journey of the Monarch butterfly is truly astounding.  Generations of butterflies return to the same over-wintering sites year after year without using any learned behaviors.  The utilization of environmental cues by multiple senses is essential to the navigation of Monarch butterfly,and disruption to these environmental cues by global warming could have harmful effects.  If you have the time, you should definitely travel down to Pismo Beach to witness the amazing collection of Monarchs that amass every year before they leave on their perilous journey north.

References

Goehring, L. and K.S. Oberhauser. 2002. Effects of photoperiod, temperature, and host plant age on induction of reproductive diapause and development time in Danaus plexippus. Ecological Entomology 27:674–685.

Guerra, P.A. and S.M. Reppert. 2013. Coldness triggers northward flight in remigrant monarch butterflies. Current Biology 23:1-5.

Heinze, S. and S.M. Reppert. 2012.  Anatomical basis of sun compass navigation I: the general layout of the monarch butterfly brain. The Journal of Comparative Neurology 520:1599-1628.

Merlin, C., R.J. Gegear, and S.M. Reppert. 2009. Antennal circadian clocks coordinate sun compass orientation in migratory monarch butterflies. Science 325:1700-1704.

Reppert, S.M., R.J. Gegear, and C. Merlin. 2010. Navigational mechanisms of migrating monarch butterflies. Trends in Neurosciences 33:399-406.

Image References

K. Kahler.  Migratory patterns of Monarch Butterflies in the United States.  Retrieved from http://www.bigsurcalifornia.org/monarchs.html.

Mexico Today.  Monarch Butterfly Migration Attracts Tourists to Michoacan, Mexico.  Retrieved from http://mexicotoday.org/natural-wonders/monarch-butterfly-migration-attracts-tourists-michoac%C3%A1n-mexico

Richard Ellis. Thousands of Monarch butterflies roost on a branch. Retrieved from http://www.richardellisblog.com/?p=109.

SK Films.  Flight of the Butterflies - Official Theatrical Trailer.  Retrieved from http://www.flightofthebutterflies.com/home/.

Accu-sane?

This is you in high school...

Hayley Chilton

Imagine you’re in high school again in the peak of puberty. You can hardly concentrate in class with that cute boy sitting in front of you.  You unconsciously spend most of the class period dreaming about how you should just introduce yourself as his next girlfriend because, let’s face it, you two would be perfect together! Well, that is if the unsightly blemishes on your cheeks disappear before he has time to notice them.

No amount of over the counter creams or medications can remedy the war zone that is your face. Not even Windex, as promised in My Big Fat Greek Wedding. You have a form of grade III acne vulgaris, also known as severe nodular acne. This type of acne can be very painful and doesn’t often respond well to medications and treatments, which can make living with it very difficult because without treatment, the condition will progress into grade IV acne vulgaris, also known as cystic acne. Both types III and IV are types of inflammatory acne.

So what are the physiological differences between inflammatory and non-inflammatory acne? To put it simply non-inflammatory acne is the result of dead cells and/or oil build-up that clog hair follicles. This type of acne is painless and usually characterized by whether or not the follicle is open (blackhead) or closed (whitehead). 

Normal hair follicle

Blackhead

Whitehead

 
Meanwhile, inflammatory acne is the result of a hormone imbalance, characterized by an elevated production of male hormones (androgens) and a decreased production of female hormones (estrogens). The increase in androgen production results in the escalation of sebum production, an oil produced by the sebaceous glands under the skin near a hair follicle. Androgen production is responsible for the elevated levels of sebum and dead skin cells shed from the follicle. These cells clog the follicle and form a plug under which sebum begins to accumulate. This inadvertently creates an ideal environment for the proliferation and survival of bacteria, which leads to the painful inflammatory lesions/pustules characteristic of individuals with this condition. Your body’s immune system will naturally respond, sending cells to fight the infection; however, this is rarely enough to “cure” nodular acne.

Nodular Acne

  Now imagine someone told you that you could eliminate this problem forever by taking a regimented dosage of oral medication over the course of several months. Don’t worry there’s only a few potential side effects which could include: nausea, muscle aches and pains, vomiting, fever, changes in hearing and vision, weight loss, liver damage, colon damage (this could be anything from the development of ulcers on your colon, to rectal bleeding, bloody diarrhea, inflammation of the lining of your colon, or the development of an autoimmune disorder in which your own body breaks down the healthy tissue in your digestive tract), miscarriages/birth defects if you become pregnant while on the drug, and depression/suicidal thoughts. Would you take it? After reading this list probably not. What if I told you the drug I just described was Accutane – a drug the millions of Americans opted to take over the last few decades.

Before and after Accutane treatment

 

So what is Accutane? Accutane is an acne medication created by Roche Pharmaceuticals. It is derivative of Vitamin A, more specifically, isotretinoin or (13cis)-retinoic acid. Therefore, Accutane is the brand name for a specific type of synthetic retinoid. Accutane was originally marketed as a chemotherapy drug, when doctors noted a marked improvement in the condition of patients’ skin. While the exact mechanism is unknown, Accutane works by reducing oil production in the sebaceous glands underneath your skin. Basically, the drug aims to trigger stem cells to differentiate into into new cells in your skin that produce less oil.

So, if Accutane is a derivative of Vitamin A, does that mean it can already be naturally found in your body? Well, not exactly…Accutane is a synthetic retinoid engineered by Roche Pharmaceuticals. However, other retinoids can be found naturally in your tissues and blood stream and can also be absorbed through the digestion of foods containing Vitamin A. Normally retinoids play roles in growth, vision, and in development – whether it’s the development of a new baby, or the development of new neurons and new neuronal connections in your brain. As with most chemical signals, in order for the presence of Accutane to elicit a functional response, the right machinery in your body needs to be present.

So let’s take a step back and make an analogy. The brain serves as the hard-drive for your body, from which several insulated wires (symbolic of your neurons) extend to different regions of your body. These wires are responsible for relaying information from the hard-drive (your brain) to different outputs (your extremities or organs). Breaking it down even further – the hard-drive can be separated into different regions in order to speed up the efficiency for which it processes information, just like your brain is divided into regions dedicated to thought, motor control, eyesight, and so forth. Given what we just outlined wouldn’t it make sense that regions of the hard-drive with more complex circuits and wire connections would be able to process more complex signals? What if I also told you that every time the hard-drive was programmed to do something new it made a new wire circuit? Well the same is true for your brain. The process of making these new neurons (wires) and new neuron connections (new circuits formed) is called neurogenesis. There is a specific region of the brain that we will be focusing on today called your hippocampus.

The hippocampus is the region of the brain associated with learning and spatial memory. So, why would scientists want to look at this part of the brain when looking at whether or not Accutane is responsible for suicidal ideology and depression? Well, the development of new neurons and new neuronal connections in this region of the brain is extremely important in order for your brain to form new memories and process information. Several studies have found that the hippocampus contains several binding proteins that bind Accutane and regulate how your body metabolizes it.

 

But, how does this relate to suicidal ideology and depression?! A study by J. Crandall demonstrated that when mice underwent long-term elevated exposure to Accutane there was a decrease in the number of these new neuron connections made. This in turn, made it harder for mice to learn! Now how on earth were they able to test that? Well, mice were initially placed in a radial arm maze and allowed to familiarize themselves/explore the maze for a given amount of time.

Mice were then trained to find a food reward in each of the given arms of the maze. Some mice were given a clinical dose of Accutane, the dose prescribed to Accutane patients, prior to experimentation. The mice that weren’t given Accutane were better able to navigate around the maze and had fewer errors when navigating than the group of mice that did receive Accutane. Therefore, results indicate a large decrease in the rate of spatial learning ability after Accutance treatment. Given that several studies have found a relationship between spatial learning ability and neurogenesis, it can be proposed that exposure to Accutane could lead to a reduction in the formation of new neurons and new neuronal connections.

Accutane usage has also been correlated with the onset of suicidal thoughts, anger and depression in several patients. While it has been proposed that a decrease in neurogenesis can be accompanied by depression, another study by K.C. O’Reilly showed that chronically administering Accutane to mice could also contribute to this behavior. Mice were again given a clinical dose of Accutane and their levels of mobility were assessed. Those that were given Accutane showed decreased levels of mobility, a behavior characteristic to an individual with depression. I’m sure anyone who has experienced depression or knows someone who has depression can relate to this concept – being depressed literally makes you want to do nothing. Accutane could thus have an influence on dopamine levels. So, how does dopamine relate to depression?

Well, dopamine is a hormone released in your brain that is associated with your brain’s “reward” system. “Rewards” increase the level of dopamine release in your brain, which leads to positive, happy, and or satisfactory feelings. Highly addictive drugs are often responsible for eliciting this response, which is why people have a hard time quitting addictive habits…because it literally feels so good! Therefore, while the direct mechanism is unknown, scientists have hypothesized that Accutane could be involved in inhibiting dopamine release. Another supportive study by Y. Sakai also perpetuates the notion that if Accutane results in a decrease in the amount of neurons formed/retained in mice, through the disruption of the normal retinoid-signaling pathway, Accutane usage may somehow be linked to depression in humans.

In 2009, Accutane was recalled from the market due to several lawsuits filed against it, with respect to birth defects, suicide, and inflammatory bowel disease. While there are several generic isotretinoin drugs available, the side effects that they cause should be taken into heavy consideration before you decide whether or not you’re willing to compromise other bodily functions for clear skin. Here we merely touched on how Accutane affects the brain, but as mentioned, there are several other ways that this drug attacks more than just acne in your body.

NOTE: In the experiments scientists used 13-ci-retinoic acid, not the brand name Accutane. However, for the sake of simplicity and conceptual understanding it was referred to as Accutane throughout this blog.

Works Cited

Cocco, S., G. Diaz, R. Stancampiano, M. Carta, R. Curreli, L. Sarais, and F. Fadda. 2002. Vitamin A deficiency produces spatial learning and memory impairment in rats. Neuroscience 115(2):475-82.

Crandall, J., Y. Sakai, J. Zhang, O. Koul, Y. Mineur, W.E. Crusio, and P. McCaffery. 2004. 13-cis-retinoic acid suppresses hippocampal cell division and hippocampal-dependent learning in mice. PNAS 101(14): 5111-5116.

“Nodular Acne: What is nodular acne and how to treat it.” Acne Hubs: A Comprehensive Guide to the Treatment and Prevention of Acne. N.p., n.d. Web. 23 Feb. 2013.

http://acnehubs.com/types-of-acne/nodular-acne-treatment/

O’Reilly, K.C., J. Shumake, F. Gonzales-Lima, M.A. Lane, and S.J. Bailey. 2006. Chronic administration of 13-cis-retinoic acid increases depression-related behavior in mice. Neuropsychopharmacology 31: 1919-1927.

Sakai, Y., J.E. Crandall, J. Brodsky, and P. McCaffrey. 2004. 13-cis-retinoic acid (Accutane) suppresses hippocampal cell survival in mice.  Annual N.Y. Academy of Sciences 1021: 436-440.

“What is Accutane? Its uses and interactions.” Drug Watch. N.p., n.d. Web 23, Feb. 2013.

http://www.drugwatch.com/accutane